1. Field of the Invention
This invention relates generally to aerodynamic drogues for aerial inflight refueling, and more particularly concerns an improved aerial inflight refueling drogue assembly having a spring loaded bleeding drogue that allows the bleeding drogue to extend as the speed increases and the load on the drogue increases, to maintain substantially constant loads on the drogue within a range of refueling refueling speeds.
2. Description of Related Art
The development of drogues for inflight refueling of aircraft has been primarily directed by the need to stabilize a refueling hose trailing from a tanker aircraft in a generally horizontal attitude. The drogue provides drag for the refueling coupling, which must resist the forward movement of a probe from a refueling aircraft. Cone shaped drogues have, proved to be suitable for low speed inflight refueling; however, it has been found that such drogues can become highly unstable at higher speeds, causing the refueling coupling device at the end of the refueling hose to become an oscillating, bobbing target, and occasionally causing the structure of the cone shaped drogue to collapse.
The high amount of drag provided by a drogue for low speed refueling also can cause the trail angle of the refueling hose and coupling to become flattened. It is desirable that the refueling aircraft not follow directly in the wake of the tanker aircraft, so that the configuration of a drogue which may be appropriate for low air speed refueling can be inappropriate for high speed refueling, even if the motion of the refueling coupling can be stabilized by aerodynamic designs.
It has therefore been a common practice to install either a low or high speed configuration drogue on the refueling coupling of a tanker aircraft on the ground, depending upon whether the aerial refueling is to take place at low or high speed, and to land to change the drogue to one of another speed configuration when an aircraft needs to be refueled at a different speed. Another approach has been to fabricate the ring shaped parachute canopy of the drogue of elastic material with openings which permit pressure modulation to provide for a constant amount of drag over varying speeds. However, such elastic openings have been found to be subject to deterioration, which can cause the amount of drag provided by the drogue to decrease over time, and can also cause an asymmetrical drag configuration to develop.
There is therefore a continuing need for a variable speed drogue which can maintain a substantially constant load on the drogue over a range of refueling speeds, and which is not generally susceptible to deterioration or damage from a refueling probe. It would also be desirable to provide a refueling drogue system that requires no modifications to a refueling tanker aircraft, and can be bolted on to a conventional coupling for conventional drogue frames and drogues, and that will permit refueling to be done from the lowest through the highest aircraft refueling speeds. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for an aerial refueling drogue that provides stability and remains inflated throughout a range of refueling speeds. The aerial refueling drogue is a bleeding type of drogue that provides substantially constant loads over a range of refueling speeds managed through movement of the refueling drogue between a retracted position and and extended position. The aerial refueling drogue system does not require modification to a refueling tanker aircraft, and can be mounted to a conventional coupling for conventional drogue frames and drogues.
The invention accordingly provides for a passive variable speed drogue for use with an inflight aerial refueling system. The refueling system includes a fuel supply, a fuel line having leading in fluid communication with the fuel supply, and a refueling coupling member connected to the fuel line for receiving a refueling probe. In one presently preferred embodiment, the passive variable speed drogue comprises a plurality of first and second support arms mounted to the trailing edge portion of the refueling coupling means, and a bleeding drogue canopy having a leading edge, a trailing edge, and a projected area. A plurality of springs operatively connect the bleeding drogue canopy between the first and second support arms, such that the bleeding drogue canopy is movable between a retracted position in which the springs are retracted, and an extended position in which the springs are extended, the projected area of the bleeding drogue canopy being variable between a maximum projected area in the retracted position and a minimum projected area in the extended position, whereby over a range of refueling speeds the bleeding drogue extends as the speed increases and the load on the drogue increases, and retracts as the speed decreases and the load on the bleeding drogue decreases, to maintain substantially constant loads on the bleeding drogue within the range of refueling speeds.
In another presently preferred aspect of the invention, the passive variable speed drogue comprises a plurality of leading edge support arms mounted to the trailing edge portion of the refueling coupling member, a plurality of center support arms mounted to the trailing edge portion of the refueling coupling member, extending radially inwardly and rearward of the leading edge support arms, and a forward drogue canopy attached between the trailing end of the leading edge support arms and the trailing end of the center support arms. A plurality of trailing edge support arms are also mounted to the trailing edge portion of the refueling coupling member, and an aft bleeding drogue canopy is connected between the trailing end of the center support arms and the trailing end of the trailing edge support arms. A plurality of springs operatively connect the aft bleeding drogue canopy to one of the trailing end of the center support arms and the trailing end of the trailing edge support arms, such that the aft bleeding drogue canopy is movable between a retracted position in which the springs are retracted, and an extended position in which the springs are extended. The projected area of the aft bleeding drogue canopy thus can vary between a maximum projected area in the first retracted position and a minimum projected area in the second extended position, so that over a range of refueling speeds the aft bleeding drogue extends as the speed increases and the load on the aft bleeding drogue increases, and retracts as the speed decreases and the load on the aft bleeding drogue decreases, to maintain substantially constant loads on the aft bleeding drogue within the range of refueling speeds.
In an alternate embodiment, a plurality of cords are attached at their origin ends to the trailing edge of the aft bleeding drogue canopy, continue respectively through each of the trailing edge support arms, and respectively up each center support arm, and through small rings attached to the inside of the aft bleeding drogue canopy. The plurality of cords are respectively attached at their other ends to the trailing edge of the aft bleeding drogue canopy at the same place where the origins of the cords are attached. As the load increases and the springs are compressed, the aft bleeding drogue canopy is gathered together at the end of the center support arms, so that the aft bleeding drogue canopy is not allowed to extend beyond the end of the drogue, reducing the amount of drogue allowed to be loose and waving like a flag, and thereby reducing xe2x80x9cflag drag.xe2x80x9d
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.